Combustion chamber with combined pulverized fuel and gas firing



April 28, 1959 l H. sElDl. 2,883,948

coMBUsTloN CHAMBER WITH COMBINED PULVERIZED FUEL AND GAS FIRING FiledAug. 7, 1952 'v 0r?v 23 45 3142]/ 23 ATTORNEY United States Patent OCOMBUSTION CHAMBER WITH COMBINED PULVERIZED FUEL AND GAS FIRING HerbertSeidl, Oberhausen, Rhineland, Germany, lassigner to The Babcock & WilcoxCompany, New York, N.Y., a corporation of New Jersey Application August7, 1952, Serial No. 303,121

2 Claims. (Cl. 110-22) This invention relates to the firing of furnacesor combustion chambers by two or more independent sets or groups ofburners involving a novel positional relationship of the two groups ofburners whereby the burners of each group can have their combustiblemixtures delivered therefrom at the particular optimum rate and with outthe firing rate of either group of burners deleteriously affecting thatof the other. In a more specific aspect of the invent-ion, each group ofburners is supplied with a different type of fuel, such as pulverizedfuel for one group and fuel gas for the other.

In the firing of furnaces with a combination of pulverized fuel burnersand gas burners, a known arrangement is to arrange all the burners inthe corners off the furnace with the pulverized fuel-air nozzles and gasburners being superposed in alternating sets with secondary airadmission nozzles disposed between adjacent sets. This arrangement isdesigned to secure mixing of the pulverized fuel flames and the gas ameson the theory that such mixing would provide optimum combustion and heatrelease conditions.

However, in practice it has been shown that such mixing of the two typesof ames results in disadvantages outweighing any possible advantagestherefrom. For example, such mixing of the flames requires that the gasbe delivered to the furnace at the same rate as the pulverized fuel-airstream is delivered. However, this gas delivery rate is unnecessarilyhigh for pulverized fuel ring. Moreover, the more rapidly burning gasrobs oxygen from the pulverized fuel-air mixture so that the slowerburning pulverized fuel remains in an oxygen-deficient atmosphere andthus burns too slowly.

While the invention principles are applicable to the firing of two ormore groups of burners with the same fuel, the invention will bedescribed with particular reference to combined firing with gas burnersand pulverized fuel burners. Thus, in accordance with the presentinvention, a combined pulverized-fue1 and gas firing arrangement forfurnaces is provided in which the ames from the two types of burners donot interfere with each others burning, and the two sets of ames admixonly adjacent the exit of the active combustion zone. Preferably, thepulverized fuel burners are arranged in one vertical zone of the furnacewith one set of gas burners beneath the pulverized fuel burners andanother set of gas burners above the pulverized fuel burners. Thepulverized fuel burners are desirably mounted in the corners of thefurnace and the gas burners in the lateral walls of the furnace at asubstantial lateral spacing from the pulverized fuel burners.

The burners are arranged to fue the furnace tangentially, the firingaxes of all the burners being tangential to the same theoreticalvertical cylinder. The tangential firing of all the burners ispreferably in the same direction, as ring in opposite tangentialdirections favors premature mixing of the burning fuel and air streamsflowing from burners delivering fuels of different characteristics, withthe aforementioned disadvantages.

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With the foregoing burner arrangement, should it be desired to re thefurnace with only one of the groups of burners, the inactive burners areexposed to heat radiation from the flames provided from the activeburners. In accordance with the invention, undue heating and harmfuleffects due to such radiation are avoided by cooling the inactiveburners by utilizing the latter to introduce cooled flue gases,preferably from the outlet flue or stack, into the furnace. Y

This recirculated gas directed into the furnace forms a blanketsurrounding the ame and thus protects the inactive sets of burners aswell as reducing radiation from the flame to the cooling tube walls ofthe furnace. In the burning of pulverized fuel alone, the enveloping ofthe ame by the recirculated gases, with consequent diminished radiantheat transfer to the wall tubes, results in at least partialcompensation for the decrease in steam temperature normally to beexpected for pulverized fuel operation as compared to gas operation. Byproper regulation of the injection of cooled flue gases, it is possibleto maintain the steam temperature substantially unchanged.

In many installations, it is desirable to fuse the fly ash, from thedischarge ues, by reintroducing it into the furnace so that it isclinkered and discharged through the ash hopper. In accordance with thepresent invention, an air stream carrying the fly ash is directed intothe furnace or combust-ion chamber tangentially to the same theoreticalcylinder to which the burner axes are tangential. The flame heated ashbecomes pasty, forms lumps, and, by virtue of its weight, is quicklycarried by centrifugal force to the cooling tube walls, where itsolidies or is clinkered and falls into the ash hopper.

For an understanding of the invention principles, reference is made tothe following description of a typical embodiment thereof as illustratedin the accompanying drawing.

In the drawing:

Fig. l is a longitudinal sectional view through a combustion chamberembodying the invention, taken along line 1--1 of Fig. 2; and

Fig. 2 is a transverse sectional view of Fig. 1 on the line 2-2 of thelatter.

Referring to the drawing the combustion chamber 10 is illustrated ashaving a substantially symmetrical polygonal cross-section with beveledcorners as indicated at 11. The lower end of the chamber is formed as anash hopper l2 having a bottom outlet which may lead to a suitable ashdisposal arrangement. The furnace gases flow upwardly through furnace orchamber 10and may be utilized to heat a steam generator (not shown).

The side walls 13 of combustion chamber 10, and the walls 14 of hopper12, desirably have their inner surfaces lined 'with a radiant heatabsorbing arrangement comprising fluid cooled wall protecting tubes 15which are connected into a lower header 16 to which are connected otherfluid conveying tubes 17. The tubes which generate steam are connectedat their upper ends to the steam and water drum of the generator andreceive water through connections (not shown) between the water space ofthe drum and lower headers such as 16. The furnace may be suitablysupported on a structural framework indicated generally at 18.

The combustion chamber 10, in the specific example illustrated, isarranged for combined firing with pulverized fuel and with gas, or witheither fuel singly. In accordance with the present invention, pulverizedfuel burners 20a, 20b, 20c, and 20d are arranged each in a beveledcorner 11 of furnace 10. Substantially in the center of each side wall13, and in a plane below the zone of the pulverized burners, is a gasburner nozzle 30a, 30b, 30e, or 30a'. A second set of gas burner nozwzles, 40a, 40h, 49C, and Mid are each arranged substantially at thecenter of side walls 13 but in a plane above the zone of the pulverizedfuel burners.

There are thus one set of gas burner nozzles 30 below the pulverizedfuel burners 20 and one set of gas burner nozzles 40 above burners 20.Also, in horizontal plan (see Fig. 2) the 'gas burner nozzles andpulverized fuel burners are arranged in alternation around thehorizontal periphery of chamber 10, the gas burner nozzles beingsubstantially midway of each wall 13 and the pulverized fuel burnersbeing located in the corners 11. All of the burners are so arranged asto lire, in the same direction, substantialyy tangentially to atheoretical cylinder Si).

Each pulverized fuel burner 20 comprises alternately arranged,vertically superposed, primary air and pulverized fuel nozzles 21 andsecondary combustion air ports 22. Fuel-air nozzles 21 are supplied withprimary air and fuel from supply pipes 23 leading from a suitablepulverizer or other source of` pulverized fuel and primary air.Secondary combustion air ports 22 are connected to secondary airconduits 24 supplied, from a suitable source, with secondary air under apositive pressure.

Gas burner nozzles 30, 40 are connected to supply conduits 31 connectedto a main 32. The latter is connected to a supply of fuel gas by a pipeor conduit 33 having a control valve 34 interposed therein. Main 32 maybe supplied with cooled flue gas, for recirculation into chamber 1t)through nozzles 3l), 40, by a pipe or conduit 35 connected, preferably,to the ue gas outlet or stack. A control valve 36 is interposed in pipe35. Additional combustion air for gas burners 30, 40, if needed, may besupplied through ports 37 supplied, from the source of secondary airunder pressure, through conduits 38.

By selective operation of valves 34 and 36, nozzles 3l), 40 may besupplied either with fuel gas or ue gas. lf desired, similar means maybe provided to selectively supply burners 20 either with pulverized fueland air or with cooled flue gas from the stack.

Fly ash, collected from the gas passes and the stack, is re-directedinto chamber 10 by a nozzle 45 arranged to direct the ash tangentiallyof cylinder 50 and in the same direction as the burner jets. The ily ashfuses together and the fused lumps are hurled, by centrifugal force,onto the wall cooling tubes where they solidify or clinker and fall intohopper 12.

In the operation of the described burner arrangement, the flames fromburners 20, supplied with secondary air from nozzles 22, burnindependently of the flames from burners 30 and 40. This is due to thevertical and lateral i spacing of the one group of burners from theother group. The llames from the two groups of burners do not mix untiladjacent the exit of the zone of active combustion in chamber 10. Hence,the two groups of burners can be fired independently as to optimumfiring rates for each, without either groupof burners interfering withthe firing of the other.

When tiring with burners 20 alone, valve 34 is closed and valve 36 isopened to deliver cooled flue gas through the idle burners 30 and 40.This flue gas forms a blanket around the active combustion zonesubstantially reducing radiation to wall tubes 15. However, the ultimatesteam temperature is not deleteriously affected as more heat is thusdelivered to other heat exchange units in the ilow path of the hotcombustion gases.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the inventionprinciples, it will be understood that the invention may be embodiedotherwise Without departing from such principles.

What is claimed is:

l. In a furnace arranged for combined ring with pulverized fuel and withgas and having side walls joined by beveled corners; sets of pulverizedfuel burners and `gas burners respectively arranged to deliverpulverized fuel-air mixtures and fuel gas into the furnace; thepulverized fuel burners being disposed in the bevelled corners of thefurnace and the `gas burners being disposed laterally substantiallycentrally of the furnace walls; the two types of burners being spacedfrom each other vertically of the furnace; all the burners tiring thefurnace tangentially to the same cylinder and in the same tangentialdirection.

2. In a furnace arranged for combined tiring with pulverized fuel andwith gas and having side walls joined by beveled corners; sets ofplverized fuel burners and gas burners respectively arranged to deliverpulverized fuel-air mixtures and fuel gas into the furnace; thepulverized fuel burners being disposed in the bevelled corners of thefurnace and the `gas burners being disposed laterally substantiallycentrally of the furnace walls; the two types of burners being spacedfrom each other vertically of the furnace; each pulverized fuel burnerincluding alternately vertically superposed primary-air-and-fuel nozzlesand secondary combustion air ports; all the burners firing the furnacetangentially to the same cylinder and in the same tangential direction.

References Cited in the file of this patent UNITED STATES PATENTS

